The presently disclosed subject matter relates to a biological signal measuring system, and more particularly to a system for identifying the blood oxygen saturation based on a biological signal acquired from a subject that is an example of the living body. The presently disclosed subject matter relates also to a biological signal measuring apparatus which is to be used in the system.
Measurement of the degree of oxygenation of blood is important for determining whether blood is sufficiently supplied to the living tissue or not. The degree of oxygenation of arterial blood, i.e., the arterial oxygen saturation can be easily measured by using a pulse oximeter. In measurement of the degree of oxygenation of whole blood including venous blood, i.e., the blood oxygen saturation, however, a NIRS (Near InfraRed Spectroscopy) sensor is usually used (for example, see U.S. Pat. No. 6,213,952).
In the case of measurement by using a NIRS sensor, optical path lengths for a plurality of near infrared light beams passed through the living tissue are varied depending on the wavelength, and a measurement result contains influences due to light attenuations caused by tissue (skin and the like) other than blood (hereinafter, such tissue is referred to as non-blood tissue). Although qualitative knowing about the blood oxygen saturation can be obtained, therefore, it is impossible to obtain a quantitative measurement value.